There are two critical factors that need to be understood when converting a vehicle from petrol to LPG:

LPG burns hotter

LPG increases the voltage requirement at the
electrode gap In an attempt to correct these two factors, as a general
rule we suggest to:

Use a spark plug that is one heat range colder than standard to
compensate for the increased heat from LPG:

The temperature profile of an engine may vary between vehicles. As
such, the effect of LPG on the operating temperature of one vehicle
may not be the same for another vehicle.

Can I use basic copper plugs and change it at shorter interval? And how about performance? Can it decrease if I am using copper plugs? And if I am using copper plugs, does it hurt to engine? At this moment I have NGK LPG LaserLine plugs

Or can I just use platinum plugs (OEM or equivalent) if engine is operating with LPG?